Biotin/lipoyl attachmentdomain has a conserved lysine residue that binds biotin or lipoic acid. Biotin plays a catalytic role in some carboxyl transfer reactions and is covalently attached, via an amide bond, to a lysine residue in enzymes requiring this coenzyme.[1]Lipoamide acyltransferases have an essential cofactor, lipoic acid, which is covalently bound via an amide linkage to a lysine group.[2] The lipoic acid cofactor is found in a variety of proteins.